Ehrlichia canis is a small, rod shaped, intracellular, tick-transmitted, Gram-negative, α-proteobacterium transmitted by the brown dog tick, Rhipicephalus sanguineus. It resides as a microcolony inside an intracellular vacuole that is membrane-lined and is mainly within monocytes and macrophages of mammalian hosts. The genus Ehrlichia is closely related to the genera Rickettsia, Anaplasma, and Wolbachia. They all share the similar intracellular structure.
Ehrlichia canis was first discovered in Algeria in 1935 and has now been known to have spread all over the United States, Europe, South America, and Asia. It causes ehrlichiosis in dogs, which is an infection transmitted by the tick. Infected dogs that are not treated can become asymptomatic carriers of the disease for years and eventually die from massive hemorrhage. Ehrlichiosis affects dogs and humans as well as other domestic and wild animal species. With global warming, expanding tick habitats and increasing international travel the spread of disease to former non-endemic areas is of great concern.
Ehrlichiosis can have multiple clinical and subclinical presentations making diagnosis challenging. Acute and chronic phases as well as co-infection with other tick-borne pathogens may further complicate therapy. Often, the pathogen cannot be completely eliminated, despite antibiotic treatment and resolution of clinical signs.
Because thrombocytopenia is a relatively consistent finding with these infections, a platelet count is an important screening test. This method of diagnosis lacks sensitivity, because low numbers of organisms make demonstration difficult. Other methods employed for Ehrlichia canis diagnosis includes blood smear, serologic diagnosis and molecular diagnosis, but each method has some limitations.
Detection of typical intracellular E. canis-morulae on blood smear examination is highly specific for ehrlichiosis. However, this method is time-consuming and not very reliable because morulae are only found in low numbers in blood smears during the acute phase of infection. Microscopy has an estimated sensitivity of 4%.
Serologic diagnosis may be helpful in identifying the presence of antibodies to Ehrlichia canis, but may not detect early infections during the acute phase of disease. The limitation of serologic diagnosis is cross-reaction, and the cross-reaction among the Ehrlichia spp. and Ehrlichia spp. is commonly recognized. Moreover, it is difficult to differentiate between post exposure and present infection.
The most current and best way to diagnose Ehrlichia canis is molecular diagnosis, especially by polymerase chain reaction (PCR) testing. PCR, which is more sensitive and specific technique, offers an alternative approach for the diagnosis of Ehrlichia canis. For example, the VetPCR Ehrlichia canis Detection Kit provided by BioinGentech is used to diagnose Ehrlichia canis infection, and it is a very fast, accurate and reliable technique. However, end-point PCR detection method, i.e. gel electrophoresis, should be combined with this diagnostic kit, and the whole procedure will take 3 hours, which is quite labor and time consuming.
Therefore, there is a need of providing an Ehrlichia canis diagnosis in order to overcome the above drawbacks.